Activation of the coagulation cascade converts soluble fibrinogen to insoluble fibrin, which polymerizes to produce, along with platelets, the haemostatic clot. Whereas the normal activation of the coagulation cascade is essential for life, inappropriate activation or failure to dissolve deposited fibrin in a timely manner may result in fibrin-dependent organ pathology. Indeed pathologically induced thrombogenesis produces venous thromboembolism (VTE), a major cause of morbidity and mortality in the USA. The pulmonary vascular compartment is a major target for VTE and other clinical syndromes characterized by fibrin deposition. However, it is unclear if the structure and mechanical properties of fibrin influences the severity of VTE and pulmonary complications. Recent studies have provided provocative new insights regarding the presence of fibrin structures with altered architecture and mechanical properties in subjects with coronary artery disease. These new findings provide mechanistic associations with the previously documented epidemiological findings between fibrinogen/fibrin and risk of cardiovascular complications. Despite similar epidemiological associations, the functional consequences and contributions of fibrin networks for the risk of developing VTE and pulmonary dysfunction remain untested. Therefore we propose that abnormal fibrin structures that are resistant to fibrinolysis induce pulmonary vascular abnormalities confer a high risk for VTE and acute lung injury. This hypothesis will be tested by: 1) Quantifying fibrin-clot turbidity, fibrin structure, fibrinolytic resistance and levels of oxidatively-modified fibrinogen in patients with clinically documented deep venous thrombosis. 2) Testing the functional consequences of thromboemboli generated from fibrinogen isolated from clinically documented DVT subjects in a mouse model of pulmonary thromboemboli challenge. 3) Ascertaining the functional consequences of fibrin generated in vivo from fibrinogen isolated from clinically documented DVT subjects in a mouse model of acute thromboembolism. Collectively these mouse models aim to evaluate for the first time the influence of variant fibrin structures in deriving pulmonary vascular complications. Successful completion of these specific aims will provide a systematic study of the biochemical and biophysical properties of fibrin clots in subjects at risk for acute thromboembolism and explore the potential biological consequences of altered fibrin assemblies in vivo.